New Cambrian big bang study defends Darwin

12 September 2013

Breakthrough method of calculating speed of evolution suggests Cambrian explosion was fast, but not implausibly so.

Museum palaeontologist Dr Greg Edgecombe and a team of researchers have created a method of measuring the speed at which animals evolved during the Cambrian 'big bang'.

The Cambrian explosion, or big bang, refers to the period between 540 and 520 million years ago when dozens of new animals appeared for the first time.

Before the explosion, most organisms were simple, often just single cells. Over some 20 million years, the first real animal life emerged, followed by more complex animals such as worm-like annelids and jointed arthropods.

Darwin's theory of evolution

In his theory of evolution, Darwin predicted that the rate at which animals develop in this way should be roughly constant over time.

Until now, the speed of evolution during the Cambrian explosion was considered too fast to support Darwin's theory. Darwin acknowledged the dilemma, which has been exploited by his opponents.

Now, for the first time, Dr Edgecombe and the team have created a reliable timeline of what external features such as hard exoskeletons, biting jaws, jointed legs and complex eyes appeared when.

They also looked at genetic changes in living animals and compared them with when the fossil record predicted their ancestors came into existence.

Fast, but not that fast

Their results show that the explosion of change during the Cambrian period happened five times faster than in any time since. This is the first time a number has been applied to the rate of change, which has previously remained vague.

'This is fast,' said Dr Edgecombe, 'but not implausibly fast'.

The novel method of measuring the evolution of arthropods. Numbers along bottom represent time before present in millions of years. Numbers along left axis are percent change per million years.

The new approach of using a morphological clock can now be applied to different scientific areas.

'Breakthroughs such as this often appear very simple once they've been achieved. Several researchers asked themselves, and us, why they hadn't thought of it,' he said.

The study's lead scientist Dr Michael Lee said that their research finally refutes arguments from some biologists that the sudden appearance of advanced animals 530 million years ago defies standard evolutionary explanation.